Use of texture analysis to study hydrophilic solvent effects on the mechanical properties of hard gelatin capsules

The aim of this work was to explore texture analysis for quantitative evaluation of the effect of hydrophilic solvent systems used as capsule fills on the mechanical properties of hard gelatin capsules. For this purpose, a texture analyzer (Stable Micro Systems, model TA.XT Plus) equipped with a capsule separating rod fixture was used. The tests were conducted in a tension mode. Elastic stiffness, tensile force and elongation at break were determined from the experimental stress–strain curve in order to quantitatively describe both brittleness and softening of capsules. In this paper, it has been demonstrated that the effect of various hydrophilic solvent (i.e. propylene glycol (PG), polyethylene glycol 400 (PEG 400), ethanol) mixtures on the mechanical properties of hard gelatin capsules can be easily monitored using texture analysis. Significant counteractive effects between PG and PEG 400 or ethanol on the integrity of capsule shells were discovered in this study. Texture analysis is found to be a convenient tool for studying formulation compatibility. It can be invaluable in early screening studies of liquid filled hard gelatin capsules.